I might be missing the point, but why send it ‘from a secret admirer’ and then be wondering whether to message him to ask if he has received it? You might just as well have put ‘Love from Gagajo’ on it.
And you say he is your part time bloke. Perhaps he thinks as he is not full time, he has another ‘part time’ admirer!
Aw, you could have fun with this. Buy yourself a Valentine card, just put a x in it and display it on your mantelpiece. Next time he comes round / Zooms / whatever, make sure he sees it, smile coyly and thank him for his card...
I sent my part-time bloke a Valentines card via an online site and signed it 'From a secret admirer.' He hasn't mentioned it yet and although I have the worlds biggest mouth, I have managed to avoid messaging him to ask him if he got it yet.
I am CERTAIN he has got it, and thinks another woman sent it. ? ? I don't know how long I can bear to leave it before telling him it was from me. Wicked, I know!