I feel you brother … (fist bump to you). Being in Love … being loyal and being all-in when it works is the greatest feeling on this planet. When there is a disconnect it is the harshest feeling ever. If you can’t talk to it or share (as a guy) … the stoic walls echo the voices and get elevated to levels that make you scream in terror.
If you partner is monogamous oriented (no shame), then desires for another person in the bed (especially if female) will be extremely threatening to them as it will be perceived as wanting to escape the relationship.
But never fear imagination is here. You need to talk to her about her crushes, the partners that make her go yum. Then you need to embrace her fantasies and not make her feel threatened, and also realize if it is a hard no … then it is a no. You will need to evaluate your relationship and intimacy.
If she has any sapphic desires, then and only then could you have a chance for the FFM experience. But you need to realize the 3rd party is there for her …. not you. It is her body and her choice. I believe Demeter deLune has a fantastic story about her being the bull if you need inspiration.
If you desire to feel some strange … then as respectfully as you can and with her consent look at wigs and dress up and setup a situation where you go into a bar separate and you have to pick her up. This may give you an idea of feeling that wild and free moment. But do understand …. she has to want to want to do this and not do this because of you ….
The inspiration for the latter paragraph came from a woman who had a husband with a strong cuckolding fetish. What she did is she had a ladies night out and she figured out the right mix of stuff to make it look like dried cum …. she even blindfolded him and tied him to the bed and made him eat her out while squirting the warmed up contents into his mouth to simulate the “pie” experience.
The point of that share and the shared partner experience is to do what you ask you will need to open yourself up and realize that the 3 way won’t be for you …. it will be for her. So you should also be prepared for a devil’s triangle in return …. what is goose is good for the gander.
You have some fantastic other suggestions ….. and toys toys toys are a great way to explore. Remember if there is shutdown from your partner (and trust me I know this very well) …. the goal is talking and growing and sharing and making her feel safe and secure ….