Girl Trouble!!!?

My Ex-GF and I just took a break. Things have been happening ever since. People say that she used me to make her ex jealous and she told me that she was going through family troubles and needed time to work them out. Then she told my sis that I loved her too much. She has been coming up with random stories and I have no clue which is true. A girl I'd liked for a long time said he wanted me to go to my friends party and thought it was sweet that I still liked her. She told my friend she wanted me to go. My EX wants to get back with me over the summer and I don't know what to do. I don't know if I should ask the girl out at the party. My Ex says she still loves and I don't know if I can believe her now and the other girl I have no clue. I haven't talked to her in a year and she randomly asked about me. I still like my ex and I like this girl. What should I do? I don't wanna make a fool out of myself.