should I trust him?? please take time to read?

[Jasmine]

Ok so this is quite long and complicated so bare with me...

The background story:
So basically my Stepmom's best friend Jo lives in Cornwall with her son who is 8 months older than me but he is in the year above me at school. When I was 6 my family went down to Cornwall for a week in the summer to stay with them. I was excited cuz my dad told me that Jo had a son who was my age and I always got along more with boys anyway. But then when we pulled up outside their house and they came out to meet us I will never forget that moment because at first the sun was in my eyes and I couldn't see them and I just heard this cute voice and I suddenly got butterflies and then I saw his face and I think that's where I first developed a major crush on him...that week we got really close and played together and wrestled on the beach and played on the trampoline with him and my stepbrothers and my stepbrothers would constantly say things like "ooo you two fancy each other" and silly stuff like that and we would cuddle on the sofa together both sucking our thumbs watching films. That week my dad proposed to my strepmom on the beach and he said to me "I want to do that to you one day and i'll put a ring on your finger". Then when we left at the end of the week I felt brokenhearted but of course being young my crush faded and I forgot all about it. Until I saw him the next year and all of those feelings came flooding back, and the next year and the next and so on... But every new year all of my stepmom's friends and their kids have a new years party and all of us kids are really close but whenever me and this boy are with all the other kids we ignore each other (although I've recently found out tho that it has always been really obvious how we feel about each other) and because I know another girl in our little group has always fancied him but he has never liked her back. Whenever we see each other we get really close and then the rest of the year we slowly lose contact. But the new year that's just gone it was the first time we were openly flirty, he kept winking at me and hugging me from behind and helping me up sand dunes when we went to the beach and throwing me over his shoulder and teasing to throw me in the sea. Then on new years eve at midnight he kissed me in front of everyone and I realised I was in love with him. The rest of the week we acted like a couple yet never actually said the words "girlfriend or boyfriend" I think because we've been close for so long and there's so much history between us we were both a bit taken aback by it all and didn't want to be put under any pressure to give what we had a label because I don't think we even know what it is. However, he kept saying things like "I will never cheat on you" and "I want to make this work" and "we can definitely keep this going even at a long distance because I love you". (it's all very cheesy yes I know) then for about the first week we were talking none stop on the phone and texting like best friends. (I'm nearly at the end stay with me) But then I noticed on his twitter he was having a lot of contact with his ex and they were constantly liking and commenting on each others posts and photos (including one where this girl is wearing only her bikini) and I know he hangs round with a lot of girls both at and out of school and recently our conversations have changed and he seems more distant and now is taking days to reply and I honestly don't mind him hanging round with other girls, I just feel like he doesn't have time for me anymore. He always tells me he loves me but then we don't speak for days but he'll post pictures of himself with other girl on social media and I constantly think about him and miss him cuz normally I'm quite guarded in relationships but because of our history I have completely let my guard down. I don't want to believe that he is like other guys but I'm beginning to question my trust in him? It's starting to interfere with my life and my happiness, what should I do?
Any advice or feedback on this situation would be greatly appreciated, thanks