how to know if a man truly love you or not
I'm not sure how you mean this.
I mean it's kinda vague in context or situation.
"How to know if a man truly love you or not" after being in a relationship with them for 5,10,20 years?
"How to know if a man truly love you or not" after emailing him for 4 months online and he typed that he "love" you in his latest email?
"How to know if a man truly love you or not" after you've been dating a while, a few months, a year, and he starts saying he loves you, how do you trust it?
"How to know if a man truly love you or not" after you've been dating a while, a few months, a year, and he never really says it, but he keeps doing incredibly loving things towards you?
"How to know if a man truly love you or not" if you're FWB and you've started developing feelings, or he seems to act like a BF but not wanting more and you want to know if he wants more?
What kind of answer are you looking for?
Some kind of "if a man 'really' loves you, then his ears turn blue, this is true for all human males at any age," that doesn't exist.
Are you looking for some kind of guarantee? Like you could take him to court and say "ah ha! this here evidence, backed up by forensic science PROVES that you love me absolutely! Now you have to live up to that, by that, and have it define you forever and ever! Ha ha! I win!" that doesn't exist.
Do you want some kind of guarantee like "I have objectively observed this man, and filled out this check list, therefore it doesn't matter what he says or does, I know he loves me," that doesn't exist and can't happen.
If you're looking for some easy means where you don't have to pay attention, learn to communicate, know who they are (maybe because you think the entire relationship is just about getting him to pay attention to and learn who you are) and rely on your own abilities, instead just be handed things, then you are pretty much screwed because you are setting yourself up as bait for "players," who would love to hand you short cuts where you can "know" they are in love with you.
Or are you just looking for some kind of confirmational bias?
Like "men can't be trusted. You never know if they love you. I need to vent about men on the internets because one just hurt me. Now I'll just read the responses that agree with that."
All those men out there can they still be trusted?
No one can be trusted, and they all can be trusted.
No one is going to put your interests above theirs unless they get something out of it.
People will always communicate the truth through their behavior and indirect communication.
The more you rely on words, and your emotional reactions to their behavior, the easier it's going to be to lie to you, and the more likely that's going to occur.
So, simply
how to know if a man truly love you or not
Learn to communicate with one that wants to learn to communicate with you.
Learning to communicate with one in no way means you've learned to communicate with them all.