His ex girlfriend

so my boyfriend of almost 6 months, his ex girlfriend is stil competely in love with him. she was the one to dump him and ever since she dumped him last year she keeps going up to him saying stuff like “we should get back together.” now my boyfriend used to be a druggie and he even went to rehab but now he is completely clean and he even quit smoking cigs because he realized that of course it is terrible for him and plus I hated kissing him, it tasted like sht. but anyways before me and him were going out his ex rachel was expecting him to ask her to homecoming. well he wouldnt because she pissed him off because she would do drugs and stuff. and he asked me to the dance and he asked me to be his girlfriend. at the end of december I got really pissed off because he was texting rachel. we were at a friends house and I saw who he was texting and I got pissed off and left him by himslef and went to go play uno with everyone else hah. and everyone kept asking me where he was. and I just replied “hes in the other room texting his ex girlfriend” I almost started crying. and he was like “I was texting her because she was sad about something” (oh and just so you know she was the one to text him first). and I just said “well everyone could care less about her” and he just said “thats a dick thing to say” and I said “so im supposed to be ok with you texting your ex who is still in love with you??” then we all left to go to a school basketball game and it was me and my boyfriend sitting in the car in the parking lot and he just started yelling at me. and I was balling my eyes out and I just got out of the car and left. when I just reached the school I got a text from my boyfriend saying “yeah ok maybe she likes me still but who gives a fuk because I dont like her like that. you think I dont care and thats not true cause if I didnt care about you then I wouldnt be sitting in this god damn car crying” I felt awfull and I went back to the car and he really was crying then I started crying as well and I said to him “youre never going to look at her, talk to her, or even acknowledge her in any way” and he repeated “I will never look at her, talk to her…etc..” and we made up everything was good but even now she still likes him and she expects that hes going to leave me and come to her rescue. and I swear she is such a stalker.. everywhere we go there she is! like we were at wal-mart yesterday to buy a cd and she was there and she sent him a text saying “soo youre looking at cd’s” I was pissed off but of course he didnt respond to her but honestly how do I get this to stop? do you think its ok for my boyfriend to be exclusive with rachel as to where theyre texting eachother? im definitely not ok with it. do you guys have any advice as to how I can make this all stop? I just want to be able to live my life with my boyfriend I love him so much and its hard when I have another girl trying to pry us apart so she can have him to herself. and btw this girl is a year younger than me. I shouldnt have to take her bulsh*t.