Do I really need to end things with him?

Hi all, I've been seeing somebody since September but we were good friends for a long time before we started dating. He and his ex were talking about maybe getting back before he and I got together and they didn't because 1. she lives cross country now and 2. he had stronger feelings for me.

I knew it wouldn't be a clean break between them but was willing to be patient because I was also at the tail end of a breakup when he and I hooked up for the first time. I stayed with him through it because he said that I was his dream girl and he wants a future with me. He also swore to be transparent about his contact with his ex.

I've since cut all ties with my ex and have devoted my time and heart to this new relationship. We have an amazing dynamic and I've never had so much fun in my life, nor have I felt so connected with somebody intellectually, emotionally, sexually, etc. In other words, he's the dream boy I never thought I'd find.

There's just one thing... He and his ex are still "friends", still text every day, she calls him when she's drunk at two AM, and has surprise-visited him twice in the time we've been dating. Both times she stayed at his house and both times he hid details of their visits from me until I asked. He swears up and down that he's faithful to me, which I really want to believe seeing as he has housemates home at all hours and the walls are paper thin. I'm also good friends with two of his housemates who would certainly tell me if something went awry while she was there. He says there's no feelings between them but last week after her second visit I saw a text from her that said "I wanna be with you".

Since october I've been asking him to end their friendship if he's truly as serious about me as he says he is. I've asked him to please talk to her about it several times and he can't seem to. I've given him the ultimatum that if their "friendship" doesn't end, I'm going to leave him. He says he understands now, after receiving that text from her, that their friendship isn't what he thought and that it's inappropriate, yet he has made no effort to shut it down, even after my ultimatum.

I'm gutted, because in my heart I know I deserve to be treated like my feelings and comfort matter but our relationship outside of this whole debacle has been so great. It seems silly to end things because of a girl that lives across the country...