Is she actively working on working towards being OK with you having other partners? In your place I'd say I was feeling chafed by the rules being different for both of us, and that I wanted to check in every 4 weeks to see if they had decided to try to be OK if I dated also. Let her know that if she needs the 3.5 months you're not taking that back, but that you'd be pretending if you acted like it wasn't stressing you out that she has a sex partner and you don't have the same freedom. (how long has it been since you said you were going to give her time?)
For me, I might give somebody more time at the end of that time 3.5 months if they weren't having sex with somebody else themselves. However, I'd find it extremely hypocritical and perhaps even cruel to be OK having a partner themselves but not agreeing it's OK for me to. Since she is, I'm guessing there's about a 85% chance I would start dating then. I'd take it slow and carefully so she could see I was trying to take her feelings into consideration and she could trust me to communicate, stick to our agreements, and understand I wasn't going to run all over her feelings in the throes of NRE.
I wouldn't "do whatever I wanted" in August either, but I'd adopt the same rules and behaviors as my partner had. If they had casual sex, I'd feel it was right for me to do so if I wanted. If they were uncomfortable with that but fine dating and romancing somebody, I'd feel that it was right for me to be able to date and romance somebody too. If they spend the night with somebody? Should be OK for me too. I would be OK agreeing to less than than equal boundaries for each of us though if I could tell my partner was making an effort and reaching outside their comfort zone. I think being willing to stay within agreements often lets people move their comfort zone rather quickly once they feel they can trust their partner.
I hope you two are able to work things out, and try not to get too caught up feeling like the situation is unbalanced, but focus on where she is trying. I don't often hear "I need time to be OK with poly so don't date yet" going hand in hand with "I am going to date while I figure out if I can be OK with you dating". I imagine some of this is based on feelings surrounding the behavior with that couple where it "appeared" you put their feelings ahead of hers, and didn't trust her opinion about what she felt happened. If you can really make her feel you wont do that again, it will probably go a long ways towards putting her at ease.
Happiness will never come to those who fail to appreciate what they already have.