Is it appropriate to Daisuki Deso to a girlfriend? Japanese language?

Question:

or is it Daisuki? or would you use aishiteru yo.

and a follow up question would i love you too be
watashi wa anata o ai shimasu?

Answer:

Use "daisuki dayo" or just plain "daisuki". For most Japanese people, "aishiteru" is too strong/affectionate and they tend to be embarrassed by it (even among spouses).

"I love you too" would be (literally) "watashi mo anata wo aishiteru" or something like that. However, under the cultural context of Japan, "watashi mo daisuki" or an equivalent expression would be more appropriate.

Of course, you can get away with violating these kinds of social norms as a foreigner. But if you want to be mindful enough of these things, avoid the use of "aishiteru".