"I love you" means very little. You need to know the person well enough to determine how they use the terms. Some guys mean nothing more than I'm DTF you. Other guys mean they would sacrifice everything to make you happy.
It depends, when l said l love you genuinely l memt that the guy made me happy, and l can see a future with him. It meant that i would stay with him till l grow old, l felt like he was a part of me. The last guy that told me he loved me said it because he wanted me to be a more submissive girlfriend, who he has sex with whenever he pleases. He was being manipulative. People say it for diff reasons, they will express ot in their actions
on the first date, I'd say run:) 2nd date - he's trying to manipulate you a ways in after you know each other and he says it so it seems true, it means he is into you and I'd view it as he's committed to you Wedding - he has to say that and he loves you right then. he has no idea what he's signing up for... Columbus sailing across the ocean kinda thing. 20 years into it - that is serious, he knows you and still loves you.. he's sticking with you. 50yrs into it - he's an idiot to still be loving you... he knows all your flaws;) that's amazing, accept your good graces 80hrs in - That's so sweet!
It doesn't change much. Many people know they love the person they are with before they even say it. When I say "I love you" to a SO, it means that I can see myself marrying her in the future. It doesn't mean I'm going to get on one knee that very moment.
To me "I love you" means exactly what it says, It means that i am committed to you and only you. I have literally said that twice in my entire life to two different women. That should give you an idea on how careful i am with it.