For example I have problems with love (not my case,just an example) and I ask the help from Aphrodite through respect by a ritual and stuff (giving offerings,making a vow etc.) but I don't keep a close relationship with her at all (but thanks are giving and offerings for the help or the vow is respected) so will this be considered disrespectful?
It won't be considered disperectfull, it's not necessary to have a close relationship with her. You can't force a connection with her or with any Deity, it comes naturally... The fact that you give her offerings and even think about that shows that you appreciate her and that you're modest.
Disrespect would be demanding aid rather than asking, thinking introvertedly/not caring about being disrespectful(you obviously care about being respectful), etc... It's hard enough to have a close relationship with someone on the Earthly plane and so many people ask such dieties for help it's not as though they can have a strong bond with every being. You seem respectful.
You can have a close relationship with the theoi, this is the point of Hellenismos. You are building a relationship with the gods through worship and sacrifice. You build it by involving them every day in your life, not because of the promise of favors or riches, but because you truly and dearly love them.
You could definitely petition Aphrodite for help in a relationship, but I do not know how much of a response you would get from her when there is no relationship between you two. It's not disrespectful, but understand she does not have to give you anything.
From what I understand of Deities it is perfectly ok to beseech a particular god no matter the connection. However, I do think it is possible to quickly develop a connection with a particular goddess or god. Also, depending upon the histories with other gods, I've found it possible to beseech certain gods through gods you are extremely close with. (I.E. asking Persephone for help with an estranged mother. And of course there's always a million different gods for various things, so you can always look it up on the internet, if you really cannot make things work with Aphrodite. But as long as you two don't have a negative relationship, you should be fine.
