As someone who identifies more with polyromantics, my opinion will probably vary from those who seek serial monogamy. Live and let live? Cool.
As long as all parties involved are aware and mutually consenting to a more open relationship, I say there is nothing wrong with it. I’m not saying everyone has to bang everyone or get married, but I am saying that having more than one partner/interest isn’t something new or bad.
However, leading people on, lying by omission and being sneaky are not ways to deal with this- if you want to date/get with both of them, put the cards on the table, be honest and see what happens.
Being open, communicative and mature is the key to enjoying and maintaining any kind of relationship, and if all parties involved are adult enough to do these things, go forth & be safe. :)