Would it be rude to stop replying and avoid someones text messages  and calls if you are not interested in them anymore ?

It is somewhat rude, but often it is very hard to say to them "I'm not interested in you anymore".  I think the kindest and most-mature thing to do would be to just write and say (lie a little), "while you seem like a very nice guy, you just don't seem to be what I'm looking for right now".

Don't voice your suspicions about honesty ... if they are being dishonest, they will deny it and try to convince you that you are wrong. And if you are merely misreading them they will think you are screwed up.  At this stage in getting acquainted, losing interest is very common and mostly to be expected (in fact, we cannot be sure if we will "work out" with someone until we have been married to them for at least 20 years).Anyone with any self-esteem and half a brain knows that if you stop replying, you have lost interest.  But if you have been dating them for a year, in person, then you SHOULD meet with them face-to-face and tell them in person.

No. You have no obligation to continue to communicate with them. Women tend to want to be kind and not hurt a guy's feelings, so you can just say that you're very busy at work and don't have time to chat. It used to be understood that people dated and got to know each other in order to find out if they wanted to spend more time together, and then maybe eventually become more serious. If you went out for a drink with someone or to a movie, there was no obligation to go on further dates, and it was "no harm, no foul". Either party could just decide that they other person wasn't what they wanted. Now people seem to think that they are instantly in a relationship. But you're not. 

Just pop a line to say, " Done. Attention turned elsewhere". nothing more than that. One and done. You don't owe strangers who swiped right a week ago any allegiance or explanation or value assessment. "Done. Attention turned elsewhere" and respond to nothing more.