I'm in love with this amazing girl, who is fully reciprocal in her love for me. We really do care for each other and have a good relationship going.
I have come to this realization that I'm a hugely possessive boyfriend. I have begun to detest the thought of her having male friends, and especially, praising the genuine good qualities of her male acquaintances. I complain to her about this, I've even termed her praise of this one male colleague of her's as "gushing on and on about him", while knowing full well that this person is totally new to her and their relationship, at best, is a working and platonic one. Yet, my behavior does suggest otherwise. I use the feeble excuse that she once, in passing, told me that praising another lady in her presence isn't chivalrous; it's not the done thing.
Although she has been magnanimous enough to excuse this indiscretion of mine one three occasions, I really feel that by repeating such behavior, I'm causing irrevocable damage to our relationship, while making her question the need to be honest with me and share her life with me. I don't want her to begin being cloistered in her conversations with me, and want her to continue to be able to be spontaneous and not guarded. I want her to be 100% comfortable with me.
Please help me in improving my character traits. It would mean a lot to me if anyone of y'all could help me be the person this girl well and truly deserves.
Cheers :)

Do you trust her? Actions speak louder than words and your actions say you do not. You need to focus on the trust you have for her, or the lack thereof. If you truly trust her, her male friends should not pose a threat to your conscience like they seem to be doing.

This isn't something changed easily and will require a lot of effort, which in turn should be very easy if there is trust for her somewhere inside you.