Friend in love with love?

My friend is 15 and states she knows what love is....she’s been in it 5 times. (Hoped you picked up on my sarcasm) she’s been dating this one boy for about 5 months now and clams she’s going to get marred to him and have kids with him. (She’s said that to pretty much all her other relationships too) But the thing is, she'll be like "I love him so much" and then 10 minutes later she'll be all sad. And when I try to cheer her up, witch gets annoying doing it 10 times a week; she just says it’s her fault. He's not abusive from what I know; he's really religious, and always telling her to read the bible and stuff. I don't know I brought it up last night and she kind of she changed subjects about like a minute of talking about it. I told her that I don’t think all the heartache is worth his “love”. They fight like no end either. At least 4 times a week if not more. She’s kind of forgets who her real friends are to, if I want to hang out, I have to tell her like 5 days in advanced and then she tells me she’ll get back to me on it then never does.(She usually just blows me off for him or someone else)) The only thing is when they break up, she'll be like "I’m going to take a break from boys" then 2 days later have a new boyfriend that she’s "in love with" and just go back to ing me on the sides just like everyone else. She doesn't really know her biological dad and her adoptive one just died a few moths ago. So I think she's trying to replace them in a way, but I’m not sure. She's been doing this before I even knew her. Help please. :]