There is no way for anyone to know whether or not you’ve had sex unless you tell them. Simply put.
Virginity is a huge topic for me (you can search for the keyword ;virginity; on my website if you want to read more) but I don’t believe in it. Firstly because of the fact that you can’t tell if someone is or isn’t one. But mostly because of the history of virginity and how it has been used to shame women who enjoy their sexuality. Which is exactly what seems to be happening to you. Fuck that giant dildo for all it’s worth. Enjoy it. Your vagina will grow and expand when aroused to accomodate it but it won’t stay stretched out. When you’re done it will go back to the size it started. If anything, think of your vaginal muscles like any other muscle. The more you use them the stronger they will get.
Lastly, masturbating and learning how to get off on your own is super extra important for when you do get around to having sex with an actual partner. You’ll know what your bodies unique needs are and you’ll be able to express them to your partner. You’ll also be able to express the sentiment “I’ve never done this before.” If he doesn’t believe you, he’s not worth sleeping with to begin with. Good luck!