Currently I am writing a Systematic Literature Review. I am aware of the systematic approach. But do the papers also constrain my discussion? Am I allowed to widen the frame by including related facts and implications in the bigger context?
Yes, absolutely; you should not be constrained; you should definitely go beyond the literature. Note that when people say "systematic literature review", they almost always mean "systematic literature search". However, following the systematic literature search, you can use any synthesis approach you want.
It is certainly expected that you faithfully report what the literature says. However, this does not mean a mere summary of each article--that is not very useful; readers could simply read the abstracts of your list of articles if that's all they want. This summary should be organized in an intelligent way that leads readers into a big-picture view of the literature that they would not easily obtain just by reading randomly themselves.
Then, beyond this--and more directly in response to your question--not only should you not be constrained by the literature, but you would help your readers even more if you go beyond the literature and add your insights that go beyond the mere summation of the literature, but bring out points that could be seen only by bringing all the literature together.