I think my Insecurities could be threatening my relationship...

Hi everyone... It's been quiet a while scince I've posted here... So much in my life has changed, I have my depression under control, changed departments at work (and earning more money) and most importantly I have met the most wonderful Man in the world.

The only problem is I have alot of insecurities and feel threatened by other females (1 in particular)..

I have been with my Bf 4.5 months now and like every relationship we have our silly little fights. But he has this girl online that he chats to online and I feel threatened by her for some reason. And I seem to pick arguments over her because of how I feel. He told me they had phone sex just after we met, which has really put me off of her, I got angry with him over that but, I have no room to talk. He tells me I have nothing to worry about cos if he wanted her then he wouldn't be with me. Which I know is true, but I can't get past the thought of him running off with someone else... I think it has to do with my ex he had 3 girls on the go while i was dating him and I guess I'm comparing my Bf to him. I know my bf would never do that he's been cheated on before and it took him a long time to get over it and start dating again. I guess what I'm asking is how do you stop feeling so insecure about something that is just in your head?

Has anyone got some advice pls..

it's hard... sometimes you can make things worse by acting or by keeping it inside.

for me it's better to let things out in the open. if i feel threatened or insecure, I deal with it and present my problem.

If that will break your relationship, then it broke because of who you are, your real concerns, and if that guy cant be with you (true you), then he is not the right person in the first place.

He doesn't want to leave me, but I worried that this will result in me pushing him away and losing him.. I have told him that I'm unsure about this girl that he chats to. He told me he's worried about losing me and doesn't ever want to lose me he hope that we get married one day. I just want to stop feeling this way..