i don’t know how to say i love you to my girlfriend

I’ve been with my girlfriend for almost a year. She frequently tells me i love you, and i can text it back but for some reason cant get the words out of my mouth. Every time i leave her house she says “i love you” and i look at her and try to say it back but i just look dumbly at her with my mouth open like i’m stupid. I love her a lot. She’s my joy in life. But i didn’t have very many friends growing up, and the ones i have now aren’t affectionate. My parents aren’t too. Those words are on the tip of my tongue but i cant get them out.

I do things for her, spend time with her, and we’ve had conversations about it and she say’s she’s okay with saying it to me and not getting anything back because she knows ill eventually be ready. But i know deep down she’s probably disappointed every time she doesn’t get a response.

I don’t know how to be ready and i don’t know how to get the feelings out. I could cry thinking about her but i can’t say three words.