^^^ A story well lived.
But treading carefully - does that mean ignoring the information OP has? Or just being careful with words when and as she speaks with her son??? (which is what I support).
Does the son’s other parent know he is engaged? What about the girl’s parents?
Any chance you can start to build a relationship with this newly engaged couple? No judgements. Just a nice relationship. Then hopefully the son will share this kind of information with you. My guess is he just was afraid of the reaction.
I want to add…I do not agree with what your son did. Regardless of the relationship you have, the family should have been notified first.
But something prevented that from happening. Maybe figuring that out…and mending some fences will help.
OP’s son is only 19. A bad marriage can be undone, but not when there are kids involved. You are a parent for life and are then tied to your kid’s other parent forever too. I would point that out to my kid if he/she were thinking about getting at such a young age.
I also think respect goes both ways, and it takes two to have a relationship. If my kid couldn’t show me the respect of informing me of such an important event, I am not sure why I would need to acknowledge it. Of course, I am assuming OP didn’t say or do anything to alienate her son.
@tucsonmom I agree +1000.
They are going to do what they are going to do.
You can either be a jerk about it and get cut out of his life, or decide to make the best of it and welcome her into the family.
Please, no FB posts. Just call him up or if he calls you tell him your friend sent the text that he was engaged. You were surprised to hear it. Let him tell you about it. Be calm and neutral.
Don’t act hurt. Don’t tell him it’s the worst thing ever. Most likely he is afraid of your reaction and didn’t tell you.
Don’t confirm his suspicions that you’d only be mad at hearing the news.
Pretty sure he’s already got your voice in his brain blaring disapproval and all the reasons it is a bad idea --which is why he didn’t tell you.
OP - My MIL never liked me but luckily FIL did … MIL thought it was a mistake for us to get married and was very vocal about it and then later passive aggressive.She died this year and yesterday was our 29th anniversary. I could write a lot more about it but the bottom line is that it caused a lot of stress for my DH and our kids over the years. It’s hard for a grandchild to love a grandparent who is not nice to their mom. Please remember in the end this is about your son’s life not yours. He may only be 19 but it sounds like he is supporting himself. Next time you see him tell him you heard from a friend he was engaged,ask him what their plans are and tell him you love him. Leave all the negative stuff out.
What about sending them an engagement card and gift?
That would communicate that you know, and that you are supportive (doesn’t indicate approval, just support.) Hopefully then he’d call to thank you, and you could have a conversation about his plans.
What? He didn’t even tell you? Any chance it could be a joke? A few years ago, everyone was posting “Married to” and “Life Partner” and all kinds of stuff with their friends. I don’t know if they do that anymore.
Could she be pregnant? I think you need to talk about this.
Another poster says something about you not visiting his page. It doesn’t matter. He could have limited any posts to be hidden from you, but didn’t think to limit the person who told you.
@MichiganGeorgia wrote
We see this also. Neither of my kids (MIL’s only 2 grandkids) feel close to her because she keeps them emotionally at arm’s length and has never been thrilled with the idea of being a grandparent. Add to that some of the things they hear her say about other people in the family (including me) and it makes her really hard to love. And boy, we try.
You all have given me a lot to think about. I haven’t really processed my feelings but mostly I just don’t care. My S has said several times that he wants to marry her, but at their age I didn’t expect this step. They have (had?) an “open relationship” which means she had boyfriends (and girlfriends apparently) in addition to S. As far as I know, he was never in a relationship with anyone else at the same time as her. This is one of the things that has really put me off, and it’s largely because I don’t want him to get hurt. It feels like an intrusive conversation to ask, “so now that you’re engaged, how does the open relationship work?”
This is why I have zero relationship with my biological grandmother. I don’t even know if she’s dead or alive and frankly I don’t care. She may be my dad’s bio mom but she’s never been my grandma.
@jeannemar, that is one question I think you SHOULDN’T ask! 
Absolutely – don’t ask and now, for your own peace of mind, you should just assume that the engagement means that they are now exclusive. I’m surprised he shared that detail with you in the first place.
Sorry- I cross posted with the OP.
Do NOT ask what their relationship is going to be like now. Believe it or not, I do know people who are in open marriages and are very happy.
I got engaged at 19 and didn’t tell my parents, even after the boy and I broke up. Recently, my daughter told my dad I had been engaged to my first boyfriend, and he was shocked! Oops.
Don’t ask that question, and for your own sanity, don’t even think about it. It may work for them and that may be all the truth that all of you need.
In situations like this, it’s good to have your H there to speak to privately about all your concerns while holding them back in front of your son. It’s hard to face that for the first time, your own child wants and needs to put someone before you and his father. It might become a more distant relationship until you all get used to it. But whether it happens at 19 or 29 this change is inevitable.
Basically, I don’t want to acknowledge the seriousness of this relationship, and since I wasn’t told directly about the engagement, I can avoid acknowledging it. I feel that the two of them are making a statement that this is their business and parents are not involved. My mom is inviting them over on Labor Day, so maybe we can have a little celebration then.
How can you celebrate if you “don’t know about it”???
It sounds like by not addressing the situation with your son, you are truly choosing to not deal with it - at all. I’m not sure how healthy that is for you if not for your son or family.
Honestly, I think I would just call and say “Hey,I hear you are engaged. Congratulations.” Then I would just let it hang out there like a big old wet noodle and wait for his response.
You will be able to judge everything by his response.
Good luck. Just don’t be negative.
OP, I think you’ve made it pretty clear why he didn’t tell you. You just said, “Basically, I don’t want to acknowledge the seriousness of this relationship…” which makes it obvious that he KNEW you’d feel this way and kept you out of the loop. You don’t seem to have a close relationship with your son, and certainly not with his now-fiance. That’s not going to go well for any of you down the road. It’s only going to get more complicated once they add children, and it could get REALLY nasty if they get divorced and you want to see the kids.
As for the open relationship, that’s not your business. At all. It’s also not unheard of and some people do make it work. I worked with a girl who was in such a relationship, then married and she was one of the happiest married people I’ve ever known-she and her husband just had dates with others. For them, it worked fine. But really, it was their business and theirs alone. We never pried about the details.