In my experience, many lesbian women don't want a man anywhere in the picture. If you do start dating a lesbian, your boyfriend will NOT be welcome to participate, watch, see pics, or even hear gory details about it later (assuming you're respectful of your new lady friend.) If he's not to be involved, you can make that clear to the women you're approaching.
There are presumably bi poly/swinger/single women (who may come with their own penis-having partners) willing throw down with you and/or you & your boyfriend. However, someone who *knows* they're bi or pan because they've had same-sex r'ships with women might not wish to be someone's experiment, or they might balk at being the first woman you've ever gone down on, etc..
I suggest you learn how to seduce women. It's a different dance, generally, & women less often approach. So I suggest you do a lot of approaching (in real life & online.) Still, you'll experience lots of rejection. Women (generally) aren't as easy to bed as men.
Once you meet your new lady friend, don't expect to lay back & she'll run the show. She may not have top energy, she might be more submissive & you will have to do the initiating. Learn your way around a strap-on & figure out if you prefer being on one end of it to another (or neither, or none.)
Possibly get specific about what you are & are not able to do for a woman. What might appeal to a queer woman about being your experimental girlfriend/secondary? Maybe get specific: You're seeking a fun potential fwb to go down on. You want a part-time girlfriend for long cuddle sessions. A unicorn for you & your bf.
Best of luck!