It would really depend on what's going on. If he's dealing with the ex only when the children need both parents attention, such as medical, I don't see a problem.

If she's buying clothes for him that's another story.

What's going on?

I used to feel like that. The longer I'm around (5 years currently) I know it will get less and less and definitely diminish to nothing. I start feeling this way when family starts talking about their past together and probably because she's pretty. So it stems from insecurity mostly. But as I said as time passes it's less and less and one day will be gone especially when our relationship duration exceeds theirs. Plus, looks only lasts so long, I'm pretty too and 10 years younger

Talk to DH about this and see how you can overcome this feeling together

I used to feel that way until I gave my dh THE ultimatum: her or me. nope, it wasn't easy and we split up for awhile until he realized that she is no longer his concern what-so-ever and that I'm the one he needs to please. now she is viewed simply as a temporary, necessary evil that needs to be dealt with OCCASSIONALLY. unless you have those appropriate boundaries in place, there is no light at the end of the tunnel.

I think it is all situational.

If the situation is that once a day BM and your DH chat/text/email for a limited amount of time and the sole focus is the kids, well, that is a situation that your feelings are probably coming from jealousy and a coping mechanism needs to be put in place.

If the situation is that BM calls/texts/emails and expects answers at the drop of a hat, she randomly stops by to drop things off, she discusses things other than the kids/relies on your DH for her own emotional support, etc., well that isn't simple insecurity, boundaries need to be put in place and it isn't a situation that you should have to accept or cope with, ever.

I think it is a normal feeling as I feel this way sometimes when the BM texts and he doesn't say anything about it. It makes me feel like he is hiding their "real" relationship as BM has no relationship or visitation with the daughter. She is with us 24/7 and the BM has no input.

So when she texts it feels like she is suddenly a part of his "private" separate life from me. Texts such as Happy Fathers Day or make sure to secure the "marital dog" on the 4th you know how he freaks out....yet it is never about SD....fortunately DF never responds.

I know the feelings are all mine but I try to put out of my head and think 1. She can't let go because she left an awesome man or 2. She does it on purpose to get at us/me. Not sure.....the only advice I can give is to ignore it or let him know how it makes you feel and if he ignores your feelings then I would think you have big problem.