If he was your boyfriend I’d say think about the relationship a bit more, but he’s the man you’re about to marry so see this as a hurdle and help him. Talk to him about it, if it’s damaging your sex life, there are ways around it to help your fiance cut down.  Keep him busy and find ways he can do so to avoid masturbating so frequently. If he has a lot of spare time, he will find a way to make masturbation a habit if he doesn’t he won’t.

This would irritate any one who was in this exact position. What you need to do is talk to her about it properly and communicate that it makes you uncomfortable and even though you know she ignores it you still find it quite disrespectful. Give it some time and be patient, the situation you’re in isn’t easy as you said. he has to have some form of contact with her, but that doesn’t give the father of her child the right to ignore the status of her new relationship. I hope it works out!

It’s only too soon if you think it is, but I will say due to coming out of a relationship recently where you dealt with abuse, you should try and get some professional therapy and counselling

You block and delete his number?

If he was sending her flirty messages while you two were together, then he’s not that serious about you. It’s either that or he’s using her as a plan B.  I’s a huge red flag also.